Abstract:

The Inner-Forcer milli-Hemispherical Resonator Gyro (mHRG) is a small, low
cost, high performance gyroscope. It may have an extremely simplified
design, with in one embodiment of the present method and apparatus only
five major parts total, with most parts filling multiple functions. The
method and apparatus in one embodiment may have: a resonator; and a body
operatively coupled to the resonator, the unitary body integrally having
electrodes, an electrode support unit, a weld ring and a plurality of
electrically conductive pins, the plurality of electrodes operatively
coupled to the electrically conductive pins.

Claims:

1. An apparatus, comprising:a resonator with a metallized inner surface;a
body operatively coupled to the resonator;a cap operatively coupled to
the body such that the cap and body form a vacuum sealed chamber that
contains the resonator;a buffer with electrical circuitry that provides,
via the body, readout pickoff signals and forcer voltages for interfacing
with the resonator; anda cover operatively coupled to the body such that
the cover and the body form a space that contains the electronics;wherein
the body functions to support the resonator and to convey the readout
pickoff signals and forcer voltages between the electronics and the
resonator.

2. The apparatus according to claim 1, wherein the body has a
substantially central aperture, and wherein the resonator has a stem that
is operatively receivable by the substantially central aperture in the
body.

3. The apparatus according to claim 1, wherein the body has a plurality of
electrodes, an electrode support unit, a weld ring, a plurality of
electrically conductive pins and a resonator electrical connection.

4. The apparatus according to claim 3, wherein the electrodes are
respectively operatively coupled to the electrically conductive pins.

5. The apparatus according to claim 3, wherein the weld ring is
operatively coupled to an outer diameter of the electrode support unit.

6. The apparatus according to claim 3, wherein the plurality of electrodes
are deposited on a surface of the electrode support unit in a
predetermined pattern.

7. The apparatus according to claim 3, wherein the plurality of pins are
hermetic feed-throughs.

8. The apparatus according to claim 1, wherein the cap has a getter
deposited on an inner surface thereof.

9. The apparatus according to claim 8, wherein the getter is activated by
heat before the sealing of the cap to the body.

10. The apparatus according to claim 1, wherein the cover provides flex
for taking up mismatch between platform and gyro materials due to
temperature.

11. The apparatus according to claim 3, wherein the body is formed from a
molded machinable ceramic part.

12. The apparatus according to claim 11, wherein the electrically
conductive pins and the weld ring are coupled onto the electrode support
unit resulting in a precision body that is hermetically sealed to
maintain a hard vacuum.

13. An apparatus, comprising:a resonator; anda body operatively coupled to
the resonator, the unitary body integrally having electrodes, an
electrode support unit, a weld ring, a plurality of electrically
conductive pins, the plurality of electrodes operatively coupled to the
electrically conductive pins, and a resonator electrical connection
operatively coupled to an electrically conductive pin.

14. The apparatus according to claim 13, wherein the apparatus further
comprises:a cap operatively coupled to the body such that the cap and
body form a vacuum sealed chamber that contains the resonator;a buffer
with electrical circuitry that provides, via the body, readout pickoff
signals and forcer voltages for interfacing with the resonator; anda
cover operatively coupled to the body such that the cover and the body
form a space that contains the electronics;wherein the body functions to
support the resonator and to convey the readout pickoff signals and
forcer voltages between the electronics and the resonator.

15. The apparatus according to claim 14, wherein the electrode support
unit has a substantially central aperture, and wherein the resonator has
a stem that is operatively receivable by the substantially central
aperture in the electrode support unit.

16. The apparatus according to claim 15, wherein the electrodes are
respectively operatively coupled to the electrically conductive pins.

17. The apparatus according to claim 14, wherein the weld ring is
operatively coupled to an outer diameter of the electrode support unit.

18. The apparatus according to claim 14, wherein the plurality of
electrodes are deposited on a surface of the electrode support unit in a
predetermined pattern.

19. The apparatus according to claim 14, wherein the plurality of pins are
hermetic feed-throughs.

20. The apparatus according to claim 14, wherein the cap has a getter on
an inner surface thereof.

21. The apparatus according to claim 20, wherein the getter is activated
by heat before the sealing of the cap to the electrode support unit.

22. The apparatus according to claim 14, wherein the cover provides flex
for taking up mismatch between platform and gyro materials due to
temperature.

23. The apparatus according to claim 14, wherein the electrode support
unit is formed from a molded machinable ceramic part.

24. The apparatus according to claim 23, wherein the electrically
conductive pins and the weld ring are coupled onto the electrode support
unit resulting in a precision body that is hermetically sealed to
maintain a hard vacuum.

25. A method, comprising:metallization of a resonator;balancing of the
resonator;metallization of an electrode support unit to form electrodes
thereon;alignment of the resonator relative to the electrodes on the
electrode support unit;bonding the resonator to the body;evacuating and
sealing; andmounting of a buffer and cover to the body.

26. The method according to claim 25, wherein the evacuating and sealing
includes getter firing, bake out and cap to weld ring sealing through
welding.

27. The method according to claim 25, wherein the electrode support unit
is formed from a molded machinable ceramic part.

28. The method according to claim 25, wherein a plurality of electrodes
are deposited on a surface of the electrode support unit in a
predetermined pattern.

29. The method according to claim 25, wherein the body has a substantially
central aperture, and wherein the resonator has a stem that is
operatively receivable by the substantially central aperture in the body.

30. The method according to claim 25, wherein the electrode support unit
has electrically conductive pins, and wherein the electrodes are
respectively operatively coupled to the electrically conductive pins.

Description:

[0002]Hemispherical resonator gyros are known and are often used as rate
sensors as part of inertial reference units (IRU's) in spacecraft and as
part of inertial measurement units (IMU's) in aircraft and land vehicles.
Much like a wine glass which rings when it is struck, the
hemispherical-resonator gyro is a precisely machined glass hemispherical
shell mounted within a protective case that is induced to ring through
the use of electrostatic forces. A rotation of the vehicle containing the
gyro will cause the location of the ringing pattern to rotate within its
case. The angle of the pattern rotation can then be detected within the
gyro to determine the rotation of the vehicle. This rotation information
is then provided to a processor which uses it to determine the
orientation of the vehicle in inertial space. The ringing vibration is so
minute that it creates virtually no internal stress and fatigue effects
in the gyro, leading to its unmatched reliability.

[0003]Miniaturization of components is an important issue for many
applications, and is especially important for spacecraft and other
vehicles where size and weight are at a premium. Ideally the
miniaturization of a component should be accomplished with no degradation
in performance.

[0004]Thus, there is a need for miniaturization of hemispherical-resonator
gyros without loss of performance.

SUMMARY

[0005]One embodiment of the present method and apparatus encompasses an
apparatus. The apparatus may comprise: a resonator; and a body
operatively coupled to the resonator, the unitary body integrally having
an electrode support unit, a plurality of electrodes, a weld ring and a
plurality of electrically conductive pins, the plurality of electrically
conductive pins operatively coupled to the electrodes, a cap integrally
having a getter, a detachable buffer circuit card assembly, and a buffer
cover integrally having a mounting ring.

[0006]Another embodiment of the present method and apparatus encompasses a
method. The method may comprise: metallization of a resonator; balancing
of the resonator; metallization of a body to form electrodes thereon;
alignment of the resonator relative to the electrodes on the body;
bonding the resonator to the body; the activating of the getter; the
welding of the cap to the body; evacuating and sealing; and mounting of a
buffer and cover to the body.

DESCRIPTION OF THE DRAWINGS

[0007]The features of the embodiments of the present method and apparatus
are set forth with particularity in the appended claims. These
embodiments may best be understood by reference to the following
description taken in conjunction with the accompanying drawings, in the
several figures of which like reference numerals identify like elements,
and in which:

[0008]FIG. 1 depicts one embodiment of the milli-HRG (mHRG) according to
the present method and apparatus;

[0009]FIG. 2 depicts a cut away view of the FIG. 1 mHRG;

[0010]FIG. 3 is an exploded cut away view of the FIG. 1 mHRG;

[0011]FIG. 4 is a perspective view of a cover that may be used in the FIG.
1 mHRG;

[0012]FIG. 5 is another perspective view of a cover that may be used in
the FIG. 1 mHRG;

[0013]FIG. 6 is a cut away perspective view of a body that may be used in
the FIG. 1 mHRG;

[0014]FIG. 7 is another perspective view of a body that may be used in the
FIG. 1 mHRG;

[0015]FIG. 8 is a perspective view of a cap that may be used in the FIG. 1
mHRG;

[0016]FIG. 9 is a cut away perspective view of a cap that may be used in
the FIG. 1 mHRG; and

[0017]FIG. 10 is flow diagram of an assembly of the FIG. 1 mHRG.

DETAILED DESCRIPTION

[0018]The Inner-Forcer milli-Hemispherical Resonator Gyro (mHRG) is a new
small, low cost, high performance HRG that may be used, for example, in
high precision hand-held targeting devices for foot soldiers. It may have
an extremely simplified design, with in one embodiment of the present
method and apparatus only five major parts total, with most parts filling
multiple functions. In such an embodiment the parts include; a resonator
with a metallized inner surface; a body having combined electrode
support, electrodes, weld ring and a plurality of electrically conductive
pins, such as hermetic feed-throughs; a cap having a getter that serves
to complete a vacuum seal around the resonator and an absorber of
residual gas in the cavity surrounding the resonator; a cover with a
mounting ring that protects electronics and provides a method for
mounting the gyro while providing flex in the attachment for taking up
thermal expansion mismatch between block and gyro materials; and a buffer
with electrical circuitry to readout pickoff signals and deliver forcer
voltages to the gyro.

[0019]The mHRG may have the performance and reliability of the proven
hemispherical resonator gyro design used in many critical space
applications for pointing and stabilization functions. Even though
embodiments of the present method and apparatus may be significantly
smaller in size as compared to typical HRG sensors, the mHRG has unique
self-calibration capability and ensures consistent performance in rugged
operational environment.

[0020]The typical HRG has extremely low rate noise, low power operation
and small size and weight. Further size and weight reductions are enabled
by the mHRG through implementation of a system mechanization that uses
only eight internal electrodes, having them provide both pickoff and
forcing functions (referred to as "inner-forcer"). This eliminates the
need for the 32 external electrodes now used on the typical HRGs.

[0021]The maximum flex amplitude of the resonator in the mHRG is read by a
pick off electrode. A force must be imposed on the resonator to make it
flex, and this is accomplished by the forcer electrode. During operation
electrostatic forces occur between the electrodes on the body and the
resonator which has a metallized surface. In this embodiment four of the
electrodes are used as forcer electrodes and the other four of the
electrodes are used as pick off electrodes.

[0022]FIG. 1 depicts one embodiment of the mHRG according to the present
method and apparatus. FIG. 2 depicts a cut away view of the FIG. 1 mHRG,
and FIG. 3 is an exploded cut away view of the FIG. 1 mHRG. FIG. 4 is a
perspective view of a cover that may be used in the FIG. 1 mHRG, and FIG.
5 is another perspective view of a cover that may be used in the FIG. 1
mHRG. FIG. 6 is a cut away perspective view of a body that may be used in
the FIG. 1 mHRG, and FIG. 7 is another perspective view of a body that
may be used in the FIG. 1 mHRG. FIG. 8 is a perspective view of a cap
that may be used in the FIG. 1 mHRG, and FIG. 9 is a cut away perspective
view of a cap that may be used in the FIG. 1 mHRG. FIG. 10 is flow
diagram of an assembly of the FIG. 1 mHRG. In the various figures like
elements are identified by like reference numerals.

[0023]A mHRG 100 according to an embodiment of the present method and
apparatus may have a resonator 108 with a stem 109; a body 105 having
electrodes 124, electrode support structure 107, weld ring 104, hermetic
feed-throughs or electrically conductive pins 112 and a resonator
electrical connection 122, between the electrically conductive pins 112,
and the resonator stem 109; a cap 106 that serves to complete a vacuum
seal around the resonator 108 having an integral getter 126; a cover 102
with a mounting ring that protects electronics, provides a method for
mounting the gyro and provides flex for taking up thermal expansion
mismatch between block and gyro materials; and a buffer 110 with
electrical circuitry to read out pickoff signals and deliver forcer
voltages to the gyro.

[0024]The resonator 108 may have, for example, a 30 mm diameter
hemispherical design. Reduced diameter resonators (i.e. 15 mm) may also
be utilized according to the present method and apparatus if a large
reduction in size is desired. While the structure of the resonator hasn't
changed from the design used in earlier gyros, the processing steps have
been reduced. With no outer forcers, the need to metallize the exterior
of the resonator is eliminated. It also eliminates the need for the
second stage of the balancing process that currently is performed after
an exterior metallization.

[0025]In one embodiment according to the present method and apparatus the
electrode support structure 107 may be constructed from a molded
machinable-ceramic part. The electrode support structure 107 may be
molded, then after firing, machined to slightly oversized dimensions.
This may then be fired a second time which results in a very strong, hard
material that will only require minimal touch-up machining for
completion. Once constructed the feed-through pins 112 and the weld ring
104 may be brazed onto the piece resulting in a precision part that may
be hermetically sealed to maintain the hard vacuum required by the mHRG
100.

[0026]The body 105 may have; an electrode support structure 107 that is
formed from a machinable ceramic material, a plurality of electrically
conductive pins 112 that extend through the body 105 at predetermined
locations, a weld ring 104, a plurality of electrodes 124, and a
resonator electrical connection 122. The electrodes 124 and resonator
electrical connection 122, may be deposited on the electrode support
structure 107 in a predetermined configuration. The plurality of
electrodes 124 and resonator electrical connection 122, also establish
respective electrical connections with the plurality of electrically
conductive pins 112. The electrically conductive pins 112 and associated
electrodes 124 provide power to the gyro, read outs from the gyro, etc.
The electrically conductive pins 112 and resonator electrical connection
122 provide power to the gyro resonator. The electrically conductive pins
112 may be hermetically sealed in the body 107. The weld ring 104 may be
formed from materials such as a high strength aluminum, Kovar or
stainless steel, and is attached to the outer diameter of the electrode
support structure 107.

[0027]The pins 112 may establish electrical conductivity with electronic
circuitry (not shown) by engaging, for example, pin sockets 114 in a
buffer 110. The electronic circuitry may be located on the buffer 110 on
a side opposed from the electrode support structure 107. The electrodes
124 may extend along the side of the electrode support structure 107 and
over the top of the electrode support structure 107 to connect with the
pins 112. In the depicted embodiment the electrodes 124 may have a
substantially wedge shape on the side of the body 107, and are
distributed around the electrode support structure 107. In the depicted
embodiment the resonator electrical connection 122 may extend along the
inner surface 117 of the electrode support structure 107 and over the top
of the electrode support structure 107 to connect with the pins 112.

[0028]The cap 106 may have a getter 126 that results in a composite part.
The cap function may be to complete the vacuum cavity enclosing the
resonator 108. The cap 106 may be welded onto the weld ring 104 while
under a vacuum such that, when the hermetic weld completely encircles the
cylinder, the vacuum cavity is sealed thereby eliminating the need for a
separate evacuation port. The getter 126 may be a heat activated type
that may be deposited in the cap 106. In one example of a getter, before
material used for the getter will work as a getter, it may be heat
activated to 450° C., and then sealed into the gyro. The getter
126 may be activated immediately before the process of welding the cap
106 to the weld ring 104.

[0029]The cover 102 may function as the protection of the electronics on
the buffer 110 under it. The side 103 of the cover 102 may be cut to
provide a spring mount that will allow the gyro to thermally expand
independently from the system platform. This prevents the thermal stress
from causing losses in the resonator 108 during operation.

[0030]The cover 102 in one embodiment of the present method and apparatus
may be formed of aluminum, Kovar or stainless steel. The cover 102 may be
attached to the weld ring 104 of the body 105 by, for example, screws or
bolts (not shown) that may extend through a first set of feet 116 on an
outer side 103 of the cover 102. A second set of feet 118 on the outer
side 103 of the cover 102 may receive screws or bolts, for example, that
secure the gyro to a platform (not shown).

[0031]In the depicted embodiment the first and second feet 116, 118
alternate around the cover 102. The cover 102 may also have a compliant
ring 122 in the outer side 103 of the cover 102. The compliant ring 122
being formed by a series of slots in the outer side 103 of the cover 102
that extends between the feet 118 and the adjacent set of feet 118. In
the depicted embodiment the compliant ring 122 has three slots that are
located adjacent the first set of three feet 118 for securing the cover
102 to the weld ring 104. The compliant ring 122 is thus an integral
structure with the cover 102. The compliant ring 122 allows for flexing
due to expansion of the platform relative to the gyro caused, for
example, by heat.

[0032]The buffer 110 may be a buffer circuit card assembly that locates
the electronic circuitry necessary to read the electrode capacitances in
the gyro. These are low level signals that would be susceptible to
electrical interference if routed from gyro to system boards. It also
provides the signal routing for forcer signals necessary to control the
gyro. The buffer 110 may have a plurality of zero insertion force sockets
or metallized pads 114 that receive and establish electrical connection
with the pins 112 of the body 105.

[0033]For example, the electronic circuitry may have buffers on the
pickoffs where the voltage that occurs across the electrodes is read out
through an op amp. These voltages may be amplified and sent out to the
system electronics. The system electronics may have analog to digital
converters that are operatively coupled to a digital signal processor to
convert the read out measurements to measurements of where and at what
amplitude the resonator is flexing. A control algorithm then sends forcer
signals out to the forcer electrodes to keep the flexing of the resonator
in a predetermined condition.

[0034]In general, a gyro is a sensor that gives information about angular
rate or how fast it's turning. Because the gyro's output indicates how
fast an object is turning, the output signal must be integrated or added
up over time. Integration involves periodically sampling the gyro with an
analog to digital converter, multiplying the resulting number by the
number of seconds between samples and adding it to a static variable that
keeps track of the angle.

[0035]Gyro bias offset, also known as the zero rate output, is the forcer
signal present when the gyro is not rotating about its sensitive axis.
For example, a gyros may have a bias offset of about 0.5°/hr. Gyro
output measurements above the bias offset indicate rotation in one
direction, e.g., clockwise, while output measurements below the bias
offset indicate rotation in the opposite direction, e.g.,
counter-clockwise.

[0036]FIG. 10 is flow diagram of an assembly of the FIG. 1 mHRG 100. The
build process for the mHRG 100 is significantly simplified according to
the present method. The overall process may be broken down into just 8
steps: Metallization of Resonator (1001), Balancing of Resonator (1002),
Metallization of Body (1003), Alignment of Resonator relative to Body
Electrodes (1004), Bonding of Resonator to Body (1005), Evacuation and
Seal (1006) (includes Getter Firing, Bake Out and Cap to Body Welding),
Top Assembly (1007) (includes mounting of buffer and cover), and Test
(1008).

[0037]It is to be understood that the parts of the gyro may have many
different shapes, and the depicted shapes are only one embodiment. For
example, the cap may be cylindrical rather than having a domed top.

[0038]The gyro according to the present method and apparatus is less
expensive to build and has less weight than prior art gyros.

[0039]The present apparatus in one example may comprise a plurality of
components such as one or more of electronic components, hardware
components, and computer software components. A number of such components
may be combined or divided in the apparatus.

[0040]The present method and apparatus are not limited to the particular
details of the depicted embodiments and other modifications and
applications are contemplated. Certain other changes may be made in the
above-described embodiments without departing from the true spirit and
scope of the present method and apparatus herein involved. It is
intended, therefore, that the subject matter in the above depiction shall
be interpreted as illustrative and not in a limiting sense.